Surgical tourniquet systems are commonly used to stop the flow of arterial blood into a portion of a patient's limb, thus creating a clear, dry surgical field that facilitates the performance of a surgical procedure and improves outcomes. A typical surgical tourniquet system of the prior art includes a tourniquet cuff for encircling a patient's limb at a desired location, a tourniquet instrument, and flexible tubing connecting the cuff to the instrument. In some surgical tourniquet systems of the prior art, the tourniquet cuff includes inflatable bladder that is connected pneumatically to a tourniquet instrument via flexible tubing attached to one or two cuff ports. The tourniquet instrument includes a pressure controller operable for automatically controlling pressure near a reference pressure in the connected inflatable bladder during a pressure control time period. Many types of such pneumatic surgical tourniquet systems have been described in the prior art, such as those described by McEwen in U.S. Pat. Nos. 4,469,099, 4,479,494, 5,439,477 and by McEwen and Jameson in U.S. Pat. Nos. 5,556,415 and 5,855,589.
Many studies published in the medical literature have shown that the safest tourniquet pressure is the lowest pressure that will stop the penetration of arterial blood past a specific cuff applied to a specific patient for the duration of that patient's surgery. Such studies have shown that higher tourniquet pressures are associated with higher risks of tourniquet-related injuries to the patient. Therefore, when a tourniquet is used in surgery, surgical staff generally try to use the lowest tourniquet pressure that in their judgment is safely possible.
It is well established in the medical literature that the optimal guideline for setting the pressure of a constant-pressure tourniquet is based on “Limb Occlusion Pressure” (LOP). LOP can be defined as the minimum pressure required, at a specific time in a specific tourniquet cuff applied to a specific patient's limb at a specific location, to stop the flow of arterial blood into the limb distal to the cuff. LOP is affected by variables including the patient's limb characteristics, characteristics of the selected tourniquet cuff, the technique of application of the cuff to the limb, physiologic characteristics of the patient including blood pressure and limb temperature, and other clinical factors (for example, the extent of any elevation of the limb during LOP measurement and the extent of any limb movement during LOP measurement).
The currently established guideline for setting tourniquet pressure based on LOP is that an additional safety margin of pressure is added to the measured LOP, in an effort to account for variations in physiologic characteristics and other changes that may be anticipated to occur normally over the duration of a surgical procedure.
LOP can be measured automatically using a distal flow sensor as described by McEwen in U.S. Pat. No. 7,479,154, or automatically using a dual-purpose cuff, as described by McEwen in U.S. Pat. No. 9,931,126.
Automatic measurement of LOP using a distal sensor, as described by McEwen in U.S. Pat. No. 7,479,154, utilizes a blood flow transducer that employs a photoplethysmographic principle to sense blood flow in the limb distal to the applied tourniquet cuff.
Automatic LOP measurement using a dual-purpose cuff has many advantages over the distal sensor method, as described in McEwen in U.S. Pat. No. 9,931,126. However, to obtain accurate and reliable LOP measurements, this method requires the use of a validated tourniquet cuff, suitable as both a sensor and an effector (dual-purpose). If a non-validated tourniquet cuff (not dual-purpose) is used, then the parameters for the LOP measurement may not be suitable, causing inaccurate LOP values that may result in bleed through or excessively high pressures applied, causing significant risk to the patient.
In addition, characteristics of the tourniquet cuff, such as cuff width and cuff length, whether the cuff is dual-port or dual-bladder, can be used to optimize the parameters for both the LOP measurement using a distal sensor or a dual-purpose cuff as described by McEwen in U.S. Pat. No. 7,479,154 and McEwen in U.S. Pat. No. 9,931,126, respectively; adjust the LOP safety margin; and change tourniquet settings, such as reducing the maximum reference pressure if the tourniquet cuff is a pediatric cuff.
Whether a cuff is a dual-purpose cuff or not, and the characteristics of a tourniquet cuff are examples of personalization parameters that are cuff-related that can be used to personalize and optimally configure the tourniquet instrument to increase patient safety. These personalization parameters may be entered manually into the instrument, which can be time consuming. Alternatively, as described in this invention, they may be read by the instrument automatically through an optical tourniquet interface.
Other personalization parameters that are not cuff-related may also be used. For instance, personalization parameters included in safety protocols can also be used to optimally configure the tourniquet instrument to increase patient safety by personalizing the tourniquet settings to the patient, the surgical procedure, or the surgeon. These personalization parameters as part of a safety protocol may include pressure and time settings, whether LOP measurement is required, LOP safety margin values, and maximum reference pressure. A user may select a safety protocol suitable for the patient, the surgical procedure, or the surgeon from a list of safety protocols to automatically configure the tourniquet settings.
In U.S. Pat. No. 9,931,126, McEwen et al. describe a surgical tourniquet system with a single channel for a single cuff. However, tourniquet systems are also commonly used with two channels for two cuffs or for a single cuff with two bladders. These multi-cuff or multi-bladder tourniquet systems are commonly used for surgeries involving intravenous regional anesthesia (IVRA) or bilateral procedures. In IVRA procedures, a dual-bladder cuff or a two-cuff system is used to retain an anesthetic agent after its introduction within a desired area. If the reference pressure levels or the inflation and deflation times of the dual-bladder cuff or a two-cuff system are not set properly, the anesthetic agent may enter the patient's circulatory system, causing serious injury or death. Tourniquet settings specifying the safe inflation and deflation times of the dual-bladder cuff or a two-cuff system can be specified in safety protocols.
In some surgical procedures, it is desirable to follow specific deflation sequences personalized to the patient, the surgical procedure or the surgeon. When a tourniquet cuff has been applied on a limb for a long duration, perioperative staff may deflate the tourniquet cuff for a short time period then re-inflate to allow limb reperfusion. A surgeon may desire a gradual stepped decrease in cuff pressure to control the release of toxins and metabolites. A procedure may also require the temporary reduction of pressure to check for bleeding at the surgical site. These deflation sequences can also be specified in safety protocols as another personalization parameter.
Safety protocols may be entered manually into the instrument, which can be time consuming. Alternatively, as described by this invention, safety protocol may be created through a remote device such as through an app on a mobile device then read by the instrument automatically through an optical tourniquet interface.
Since different tourniquet instruments may use different methods of determining LOP, and regulate pressure, due to hardware and/or software differences, personalization parameters described previously may be suitable for optimally configuring one type of tourniquet instrument but unsuitable or hazardous for another type of tourniquet instrument. For an example, personalization parameters intended for a single-port tourniquet instrument would not be suitable for a dual-port tourniquet instrument. Furthermore, configuring a tourniquet instrument by reading personalization parameters, such as those contained in a safety protocol, may be hazardous in certain situations, such as when the cuff is pressurized during a surgical procedure.
Therefore, there is a need for an apparatus and method to acquire personalization parameters to optimally configure a tourniquet instrument to increase patient safety by personalizing the tourniquet settings to the patient, the surgical procedure, or the surgeon, only if the personalization parameters are intended for the tourniquet instrument.
Some surgical tourniquet systems of the prior art include means for configuring the tourniquet instrument through cuff identification. McEwen in U.S. Pat. No. 6,682,547 describes a cuff identification method in which the tourniquet instrument detects cuff connectors having different colors that are indicative of the physical characteristics of the cuff, after the cuff and the instrument establishes pneumatic connection. This method has several limitations: (1) the color detection is performed at the cuff connector which is away from the instrument. Thus, the hardware used for detection is carried on the pneumatic tubing connected to the instrument and is more susceptible to damage as the pneumatic tubing may be dropped onto the floor, stepped on, or come in contact with liquids such as blood and cleaning solutions; (2) the number of detectable colored connectors are limited by their distances from each other in color space. The greater the number of different colored connectors there are, the closer they are to each other in color space, and the more likely it would be for false positives under different lighting conditions, or as the color degrades over time or due to cleaning chemicals. Therefore, the number of different cuffs that can be identified and the amount of data that can be contained in the colored connectors are limited; and (3) cuff detection requires physical contact between the cuff and the instrument through the connectors which may be hazardous if the cuff is sterile and must remain sterile.
Contactless cuff identification through RFID is described by McEwen in U.S. Pat. No. 9,931,126. However, RFID cuff identification has limitations: (1) RFID tags are susceptible to malfunction upon irradiation commonly used to sterilize tourniquet cuff assemblies; (2) misidentification may occur when more than one cuff with a different RFID tag is in close proximity to the RFID reader; and (3) RFID reader and RFID tags may incur a substantial increase in the cost of the instrument and/or the tourniquet cuff.
Other cuff identification apparatus and methods described or suggested in the prior art may have high risk of malfunction, be unreliable, add substantial cost, have limited number of cuffs that can be identified, and/or create legacy issues.